In 1967 the American counterpart to a global motorcycle manufacturer requested the development of a vehicle that its dealers could sell during the winter season of slackening motorcycle sales. The result was the introduction of a three-wheeled all terrain vehicle (ATV) which debuted in 1970. This original ATV exhibited a tricycle geometry and employed a seven horsepower motorcycle engine to drive two rear twenty-two inch low pressure tires through a dual-range, four-speed gear box with an automatic clutch. The machines handled snow, mud and various slippery conditions which a motorcycle couldn't.
Further development optimized tire and chassis design. While then primarily a recreational device, farmers saw substantial utility in the ATV. In this regard, a farm tractor costs exponentially more than an ATV and a typical ATV utilized 8% of the fuel consumed by such a tractor. This multipurpose usage grew from about 30% of total usage to about 80% total usage in the current market. The other major ATV interest in the 1980s was racing everywhere from frozen lakes in the East to Western dessert to the dirt ovals of Middle America. Four-wheel machines were introduced in 1984 and were considered more versatile, particularly for utilitarian use. Inevitable accident statistics prompted the Consumer Product Safety Commission (CPSC) to mandate a four-wheel design. By 2001, the ATV industry was selling about 400,000 units per year.
Two basic types of ATVs have evolved to suit the needs of riders. These include: sport models referred to as “sport quads” which are used by high performers, for instance, in racing and to some extent by casual recreationists and utility models used for a wide range of work and recreation activities.
Utility models typically incorporate four-wheel drive and will weigh about 400-500 pounds. Sport quads incorporate two-wheel drive, somewhat expensive suspensions and more refined motors. Typically weighing about 370 pounds, these sport vehicles are quicker and more responsive than the utility models. Just as in essentially all forms of automotive racing, the talent of the driver is quite important. For instance, with two-wheel drive, when beginning a turn, a bit more throttle is employed and a slight “slide” of the rear wheels is developed. Thus the type of terrain on which the vehicles are driven has a high importance with respect to racing technique and generally varies from racing venue-to-venue.
As may be expected, sport quad racing also calls for a tuning of front end suspension which is characterized preferably with optimization for each track. For instance, the two front wheels are suspended from ball joints, in turn supported by upper and lower A-frames or control frames pivotally mounted to the chassis with rod end Heim joints. For a highest level of performance at each racing venue, experienced mechanics will adjust these suspensions for caster and camber. Caster is the angle between a vertical line and the ATV's steering axis when viewed from the side. It is measured in degrees and minutes. Negative caster generally gives more steering going into a turn, but less coming out. Positive caster gives less steering going into a turn (initial steering), but more steering as the vehicle exits. Caster is adjusted to provide more stability on straightaway performance.
Camber, as seen from the front and rear of the ATV is the angle of the tires in relation to the ground. Tires that are perfectly perpendicular to the ground (90°) are said to be at “zero camber”. If the tops of the tires lean toward each other, the tires have negative camber, and if they lean out, the tires have positive camber.
While camber can be tuned by bolt and nut adjustment at the upper ball joint, caster cannot. Typically, caster is adjusted by removing the upper A-frame structure and making an adjustment at the rod end Heim joint. Unfortunately, that form of adjustment also affects camber. Accordingly, a substantial amount of talent is required for making a caster adjustment. An improved caster adjusting mechanism was introduced by Houser, et al, in 2005. Sold under the trade designation “Slicast™” and described in application for U.S. patent Ser. No. 11/266,697 filed Nov. 3, 2005, the mechanism employs indexably rotatable ball joint threaded stud supports having an eccentric stud-receiving open shaft. This provides a repeatable and simplified caster adjustment over a range of positive and negative values.
While such improved caster adjustment mechanisms and techniques have been very beneficial in pre-tuning vehicle suspensions with respect to a given racing venue, essentially all such venues exhibit a topography of both racing turns and straightaway runs. While caster can be optimized prior to a race, its resultant adjustment generally will remain a compromise between more negative caster for turns and more positive caster for straightaway runs.